WASHINGTON — Massive refugee migrations, bloody conflicts over water and other essential resources, and the U.S. military called in for huge relief efforts or as peacekeepers — this is one global prediction if governments don’t curb greenhouse-gas emissions.

Because that warning is coming from a growing number of retired generals and security experts, the notion that dealing with global warming is a national-security imperative that requires international cooperation is gaining currency as Congress debates legislative remedies.

Using the military’s risk-assessment practices, 11 retired generals and admirals issued a recent report saying that climate change is a “threat multiplier” that makes instability worse in Asia, the Middle East and Africa, and could spark a greater refugee flow into Europe.

Their warnings are having an impact, from Congress to intelligence agencies and the Pentagon. One of the retired generals, former Army Chief of Staff Gordon Sullivan, said “it’s not a hard sell” because the Defense Department already is assessing instability around the world.

“The impacts of climate change will be huge — deserts move north, coastal areas threatened, the dislocation of people,” said retired Adm. T. Joseph Lopez, who commanded peacekeeping forces in Bosnia. “I’m a student of instability, and instability is the enemy. It helps religious extremists and terrorists.”

The former military leaders urge the United States “to commit to a global partnership” to reduce carbon dioxide and other emissions and to help developing countries deal with climate change.

The House voted two weeks ago to direct intelligence agencies to conduct a formal assessment of the impact of climate change. Rep. Anna Eshoo, a California Democrat and member of the Intelligence Committee, requested the study in an intelligence spending bill after she read that the retired military chiefs recommended it.

“When you have a former Army chief of staff and Gen. Tony Zinni (former commander of Central Command in the Middle East), people know it’s serious, that this is a national-security threat,” Eshoo said.

Some House Republicans warned that focusing on global warming could distract agencies from the threat of terrorism, or suggested it was a marketing ploy designed to help military and intelligence officials defend bigger budgets. Some belittled the initiative.

“Let other federal agencies cover the bugs and bunnies, but let our spies be spies,” said Rep. Pete Hoekstra, a Michigan Republican and former Intelligence Committee chairman.

The “bugs and bunnies” comment was a reference to former CIA Director George Tenet, who said some analysts used that disparaging label when Vice President Al Gore requested studies on climate change in the late 1990s.

But times have changed. Michael McConnell, director of national intelligence, wrote Eshoo that “it’s entirely appropriate” for intelligence agencies to assess “the geopolitical and security implications of global climate change.”

McConnell’s statement and the vote in the House “were good indications that people see this as important,” said Sullivan, a former member of the Joint Chiefs of Staff.

The military leaders warned that climate change already is having an impact on such crises as Somalia and Darfur, and causing more Africans to flee to Europe. Lopez warned that even stable governments, such as Turkey and Syria, could “one day go to war over water.”

The voice of military leaders is an important new element in the climate-change debate, environmentalists say.

Russell Train, a longtime leader of the environmental movement, said activists “could easily be dismissed as the fringe, or a group of elitists, but that’s not the case with the military leaders, so it’s refreshing to see them speak out.”